Some campuses that just opened for the new year are closing because of heat.

In Virginia’s Pulaski County public school district, two campuses closed early Friday because of “extreme heat,” officials said.

In Baltimore City, where extreme weather in summer and winter has long created problems for aging and cash-strapped schools, the teachers union is seeking donations to buy hundreds of fans for the beginning of the school year Sept. 3.

The 2019-2020 academic year is just getting started, and already schools throughout the country are facing a big problem: searing heat and classrooms without air conditioning. It’s not just about comfort, researchers say, but about teachers and students being able to do their best work.

“If we want our students to do their very best, to tackle and master rigorous content, to imagine creative solutions to the complex problems of our world, we need to provide them with an environment where they can focus on the task at hand, rather than the sweat beading on their foreheads,” the Baltimore union said in appealing for donations on its website. It noted that schools’ internal temperatures have been measured at more than 100 degrees.

In Memphis, schools opened Aug. 12 amid an excessive heat warning issued by the National Weather Service as the heat index — what it feels like when humidity is factored in — rose above 110 degrees, hitting 115, and at least one campus closed. Athletic teams could not practice outdoors because the Tennessee Secondary School Athletic Association says no outdoor practice should be held if the heat index is above 104 degrees.

In Georgia, a 16-year-old female basketball player died following a conditioning drill at a Clayton County school during extreme heat. The Atlanta Journal-Constitution said the temperature reached 100 degrees that day. It also said the Georgia High School Association, the governing body for sports, prohibits outdoor workouts at 92 degrees. The cause of the student-athlete’s death is unknown.

School districts maintain their own weather guidelines, and officials — and sometimes principals — can make decisions on a case-by-case basis.

In the Montgomery County Public Schools in Maryland, there can be no activities outside or in facilities without air conditioning when the heat index hits 105 degrees. The same is true for the Loudoun County Public Schools district in Virginia. But in the Sherman Independent School District in Texas, conditioning exercises are not moved indoors until the heat index reaches 110 to 115 degrees, according to its policy.

While many districts — including D.C., Fairfax County and Loudoun County public schools — have air conditioning in all of their schools, many systems don’t.

In Baltimore County’s school system, only six campuses lack air conditioning: two high schools, three elementary schools and a charter school, a spokesman said. Fans are used when necessary, students are allowed to carry water bottles, and schools are closed if it gets too hot. That happened in September, when schools without air conditioning were closed for the first three days of the 2018-2019 school year.

Researchers say student learning can be affected when it gets too hot. In 2012, striking Chicago teachers made classroom air conditioning one of their demands, saying students and teachers can’t do superior work when the temperature is nearing triple digits.

Numerous studies link the quality of school facilities to student achievement, and some researchers say maintaining a comfortable classroom temperature is crucial.

R. Jisung Park, assistant professor of public policy at the University of California at Los Angeles and associate director of economic research at UCLA’s Luskin Center for Innovation, co-wrote a soon-to-be published paper titled “Heat and Learning” that argues that heat is such an important factor that it could contribute to the achievement gap. In an op-ed Park wrote in USA Today, he said:

The effects of heat on learning are more pronounced for African-American and Hispanic students and for those living in poorer neighborhoods. School air conditioning is unequally distributed: Black and Latino students are significantly more likely to report inadequate air conditioning. For them, a 90 degree school day has a negative effect on learning that is nearly 2 1/2 times what it is for white students.

The Baltimore Teachers Union said as much in its appeal for fans: “It’s no secret that Baltimore’s students have had to weather the spectrum of extreme temperatures in their classrooms. We’ve all seen the photos of kindergartners sitting in their coats and mittens at their morning circle. The reverse is true when school is back in session at the end of summer, when schools’ internal temperatures have been measured at over 100 degrees. The Baltimore Teachers knows that educators’ working conditions are students’ learning conditions.”

Whether schools can actually use the fans is another question. As the Baltimore Sun reported, some school system officials expressed concerns that the electrical systems of old school buildings can’t handle the additional demand imposed by fans.

The Pulaski County public schools district in Virginia posted this Friday on its Facebook page, as temperatures came close to 90 degrees: “Pulaski Middle School and Dublin Middle School will dismiss 2 hours early today due to extreme heat in the classrooms. All other schools will remain on their regular schedules.”

In New Mexico, the Albuquerque Journal reported that teachers and students already back at school and in classrooms lacking air conditioning are complaining about the heat, which has reached into the 90s. It quoted Tomás Sánchez, a social studies teacher at Washington Middle School, saying the heat is debilitating.

“It takes a lot longer for me to get that job done,” Sánchez said. “There’s a lack of focus, and you start to get drained faster.”

And here are some thoughts about it from social media:

schools should be required by law to start after labor day. especially when a lot of schools don't have the proper air conditioning for the heat. kids are gonna be uncomfortable and unable to focus when they're sweating to death in their classrooms